Apparently my 'easy' isn't the same as yours. There's nothing I could find in the code that describes what it is. You'd have to make a pretty big logic leap to figure it out. All you can see in the code (in config.js, not in index.html) is the dataset url (random string) and the description "this website", which tells you very little.

For anyone who just wants to skip to the answer, I found it in the pull requests / issues: https://github.com/ClickHouse/adsb.exposed/issues/47

Interestingly it seems to line up quite well with population density maps.